The present invention relates to a method and a circuit for signal amplification in digital hearing aids, in particular in hearing aids with automatic gain control (AGC).
As prior art, it is known to use algorithms for the amplification of input signals in digital hearing aids, which algorithms simulate the charging and discharging behavior of an AGC capacitor element in an analog hearing aid. The sampled values obtained from analog input signal values by digitization are compared with a stored mean sampled value, and, if necessary, are smoothed in case of deviation from this mean sampled value. The waviness of the sampled values is thereby reduced. Corresponding stored gain values are thereupon allocated to the smoothed sampled values. By combining these gain values with the possibly pre-processed sampled signal values, different kinds of signal compressions, signal expansions, or a combination of the two can be produced. After reconverting the sampled digital signal to analog, a correspondingly amplified output signal results.
However, a substantial and undesirable increase in the harmonic distortion of the output signal in relation to the input signal is to be noted with such a smoothing and subsequent amplification of the input signal.